At present the Physical Uplink Control Channel (PUCCH) Format 1b with channel selection can be adopted in a Long Term Evolution Advanced (LTE-A) system with Carrier Aggregation (CA) as a multiplexing transmission scheme of an Acknowledge (ACK) character or a Negative Acknowledge (NACK) character. A dynamic channel resource reserved on an uplink primary component carrier shall be made best use possible of in order to reduce the overhead of uplink control channel resources; the state of multiple-to-one ambiguity in an ACK/NACK mapping table shall be avoided in order to avoid unnecessary retransmission in the system and to improve the throughput performance of the system; and the ACK/NACK mapping table may be applied to both an across-carrier scheduling scenario and a non-across-carrier scheduling scenario in order to reduce the complexity of a standard when an across-carrier scheduling is supported by the LTE-A system, and different channel resources may be required when a User Equipment (UE) transmits ACK/NACK using the PUCCH Format 1b with channel selection in the across-carrier scheduling scenario and the non-across-carrier scheduling scenario.
For a long term evolution multi-carrier system, a higher system bandwidth, for example, a 100 MHz system bandwidth, than a bandwidth of an LTE system can be allocated directly for the system in order to support the 100 MHz system bandwidth as illustrated in FIG. 1; alternatively, all or a part of a spectrum allocated can be aggregated, i.e., carriers can be aggregated, into the 100 MHz system bandwidth for provision to the long term evolution multi-carriers/system as in FIG. 2, in which case uplink and downlink carriers may be configured asymmetrically in the system, for example, a user equipment can occupy N (N≧1) carriers for downlink transmission and M (M≧1) carriers for uplink transmission.
At present aggregation of at most 5 carriers can be supported in the LTE-A system, and a UE in the LTE-A system has to feed back ACK/NACK feedback information corresponding to a plurality of downlink carriers and downlink sub-frames in the same uplink sub-frame. In the LTE-A system, ACK/NACK information of no more than 4 bits can be transmitted using the PUCCH Format 1b with channel selection. With the PUCCH Format 1b with channel selection, the UE selects one channel resource among a plurality of channel resources (i.e., candidate channel resources as required) for transmission to distinguish different ACK/NACK feedback information states, where an ACK/NACK mapping table is used for a mapping relationship between ACK/NACK feedback information, real channel transmission information (that is, 4 constellation points with QPSK modulation in the PUCCH format 1b, i.e., QPSK modulation symbols) and a selected channel used to transmit the real channel transmission information. For example, 2, 3 and 4 uplink control channel resources are required for the transmission of 2-bit, 3-bit and 4-bit ACK/NACK feedback information respectively.
At present, all of channel resources used for the transmission of ACK/NACK feedback information using the PUCCH Format 1b with channel selection are dynamic channel resources in the Long Term Evolution (LTE) system, where a dynamic channel resource refers to an uplink control channel resource, reserved on an uplink carrier, for each Control Channel Element (CCE) in a control information region of a corresponding downlink carrier in pair with the uplink carrier. The UE calculates and obtains one available uplink control channel resource from the lowest CCE index of each Physical Downlink Control Channel (PDCCH) transmitted on the downlink carrier, that is, each PDCCH corresponds to one available uplink control channel resource of the PUCCH formats 1/1a/1b, and such a resource is referred to a “dynamic channel resource” or an “implicit channel resource”.
In the LTE-A system, the dynamic channel resources reserved on each Up Link Component Carrier (UL CC) are only for the PDCCH on a DL CC paired with the UL CC, and a PUCCH can only be transmitted on an Up Link Primary Component Carrier (UL PCC), so a dynamic channel resource is only present on an UL PCC from the perspective of the UE, and since the UL PCC reserves a dynamic channel resource only for a Down Link Primary Component Carrier (DL PCC) corresponding to the UL PCC, that is, a dynamic channel resource is only present for a PDCCH transmitted on the DL PCC, not all the channel resources required for the transmission of ACK/NACK using the PUCCH Format 1b with channel selection may necessarily be obtained from dynamic channel resources. As illustrated in FIG. 3 where 2-bit ACK/NACK feedback information is transmitted using the PUCCH Format 1b with channel selection, and when no across-carrier scheduling is supported in the LTE-A system, the UE can only obtain one dynamic channel resource from the UL PCC (i.e., the UL CC1), and since the DL CC2 is not a PCC, a dynamic channel resource on the UL PCC cannot be obtained from a PDCCH transmitted on the DL CC2 and thus a higher-layer semi-statically configured channel resource is required. Further as illustrated in FIG. 4, 4-bit ACK/NACK feedback information is transmitted using the PUCCH Format 1b with channel selection, and even if across-carrier scheduling is supported in the LTE-A system, the UE can only obtain one dynamic channel resource respectively from an UL CC1 and an UL CC2, so 2 additional semi-static channel resources are required for the UE to transmit the 4-bit ACK/NACK feedback information using the PUCCH format 1b with channel selection.
The method for obtaining the channel resource and the type of required channel resources may be different respectively in different scheduling scenarios when the UE transmits ACK/NACK feedback information using the PUCCH Format 1b with channel selection. Thus an ACK/NACK mapping table shall be designed based on the type of the channel resource. For a downlink carrier using a dynamic channel resource, the UE can not obtain a corresponding dynamic channel resource when a PDCCH scheduling the carrier is lost, and this state is represented as Discontinuous Transmission (DTX), and thus, feedback information states of the UE for the downlink carrier include ACK (to characterize correct reception of a data packet), NACK (to characterize wrong reception of a data packet) and DTX (to characterize a data packet being lost or not scheduled), which means that an ACK/NACK mapping table shall satisfy the followings: when the feedback state for the downlink carrier is DTX, an ACK/NACK/DTX combination state to be fed back from the UE can not be transmitted on a channel resource corresponding to the carrier. For a downlink carrier using a higher-layer semi-statically configured channel resource, there is always an available channel resource present regardless of whether a PDCCH scheduling the downlink carrier is lost or not, and at this time, an ACK/NACK/DTX combination state to be fed back can be transmitted on a channel resource corresponding to the downlink carrier regardless of whether the feedback state of the downlink carrier is DTX or not.
In summary an ACK/NACK mapping table shall be designed by taking into account the type of the channel resource in use, and there are a large number of ACK/NACK/DTX combination states in an ACK/NACK mapping table with all the channel resources being dynamic channel resources. Taking 4-bit ACK/NACK feedback information in the LTE system as an example, there are 19 ACK/NACK/DTX combination states, but at most 16 states can be distinguished by 4 channel resources and 4 constellation points with QPSK modulation, so there may be an overlapping mapping between different ACK/NACK/DTX combination states, and in this mapping scheme, a base station can not determine the actual state of ACK/NACK fed back from the UE, thus resulting in an increased number of retransmissions in and a lowered throughput of the system.
The use of a dynamic channel resource may also result in an increased number of ACK/NACK/DTX combination states despite an increased utilization ratio of an uplink channel resource of the UE, thus complicating the ACK/NACK mapping table and possibly degrading the performance of the system due to a shorten distance or an overlapping state between codewords corresponding to different ACK/NACK/DTX combination states; and the use of a higher-layer semi-statically configured channel resource may result in an increased overhead of uplink control channel resources although the number of ACK/NACK/DTX combination states can be reduced to some extent to thereby increase the distance between codewords and avoid an overlapping state between codewords and thus improve the performance of the system.
Thus a current interesting technical problem is how to allocate an uplink channel resource for transmission of ACK/NACK feedback information to thereby improve the performance of the system while taking a resource overhead of the system into account.